1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a home network. More particularly, the present invention relates to a method of synchronizing a plurality of content directory service (CDS) devices, and a CDS device used in the synchronizing method and a system thereof.
2. Description of the Related Art
Generally, a home network is formed of a private network based on the Internet Protocol (IP), and controls various devices such as personal computers (PC), intelligence products and wireless devices by connecting them as one network through a common virtual computing environment.
Middleware makes communication between devices possible by connecting various digital devices in a peer-to-peer manner, and home AV interoperability (HAVI), universal plug and play (UPnP), Java intelligent network infra-structure (Jini), home wide web (HWW), and others have been suggested for the middleware.
In a computing environment established through the UPnP middleware, each device is allocated an address according to the dynamic host configuration protocol (DHCP), or is allocated an address selected by the automatic IP-specifying function (Auto IP), through which communication between devices, and retrieval and inquiry on the network are performed.
The UPnP network is a home-network technology that is projected to be widely used in the near future, and defines the UPnP device and the UPnP service, and is defined by the protocol between them. The UPnP network is constituted by a controlled device (CD), which is a home-network device connected to and controlled by the home network, and a control point (CP), which is a device for controlling such a CD. The CP controls the CD, and requests and receives events. The CD performs specified functions according to the request of the CP, and when the state of the CD is changed, the CD sends the event to the CP that has requested the event.
The operation of conventional UPnP network devices includes an advertisement process, a discovery process, a description process, a control process, and an event process.
In the advertisement process, a new CD is connected to the home network, and informs other devices in the home network of its presence. In the discovery process, a new CD is connected to the home network, and discovers CDs operated in the home network. In the description process, the CP parses a service-description XML file or a device-description XML file using the IP address of the CD acquired in the discovery process, and recognizes the functions of the added device in detail. In the control process, in the case where the CP intends to provide a certain service using the CD, the CP transmits a control message (action request) that requests a predetermined service to the CD using simple object access protocol (SOAP) according to the UPnP device architecture, and receives a response message to the control message (result, a variable value). In the event process, the state of the information change of the CD, which has provided a predetermined service by the control command transmitted from the CP, is checked.
The UPnP AV technology, which allows a user to enjoy multimedia content such as audio and video content based on UPnP technology, is described in the UPnP AV specification. According to the UPnP specification, the UPnP AV architecture consists of a media server that provides multimedia files through a content directory service (CDS), a media renderer that replays the provided multimedia files, and a CP that controls the media server and the media renderer so that they operate together. The CDS is built in the media server, and provides metadata of content existing in the home network or stored in the media server to the CP. The CP checks the metadata from the CDS, and requests the media renderer to replay it.
In the case where there are multiple devices that constitute the above-described UPnP AV architecture in the home network, multiple media servers that store different content, and multiple CDS exist. In such a UPnP AV environment, there is a need for a method where the user of the UPnP AV synchronizes a certain CDS with different CDS. That is, there is a need to synchronize content scattered in different CDS. Here, the synchronization means that content held in each CDS and the metadata are exchanged between CDS according to a certain policy specified by the user. For example, if content stored in a device such as a MP3 player is synchronized with the home media center, the user can enjoy high-volume sound using a Hi-Fi device existing in the home.
However, in the case where a plurality of CDS participate in synchronization, the CP has to play many roles such as collecting logs and determining CDS pairs to participate in synchronization, and as the number of CDS that participate in synchronization increases, the number of synchronizations rapidly increases, both of which are problems.